WO2009153248A2

WO2009153248A2 - Adhesive connection of folded honeycomb cores in sandwich structures

Info

Publication number: WO2009153248A2
Application number: PCT/EP2009/057415
Authority: WO
Inventors: Thomas Meer; Wolfgang Summa; Georg Wachinger
Original assignee: Eads Deutschland Gmbh
Priority date: 2008-06-19
Filing date: 2009-06-16
Publication date: 2009-12-23
Also published as: DE102008028864A1; DE102008028864B4; WO2009153248A3

Abstract

According to an embodiment of the invention, a sandwich structure having a folded honeycomb core is produced by applying an adhesive to the honeycomb webs of the folded honeycomb core and then positioning it in a targeted manner so that the adhesive in a first area is reduced and is supplied to a second area where it is collected. The positioning of the adhesive is for example brought about by magnetic forces or hot air.

Description

Adhesive bonding of folded honeycomb cores in sandwich structures

FIELD OF THE INVENTION

The invention relates to sandwich structures. In particular, the invention relates to a method for producing a sandwich structure with a folded honeycomb core, a tool for producing a sandwich structure with a folded honeycomb core, a sandwich structure for an aircraft and an aircraft with a sandwich structure.

TECHNICAL BACKGROUND

Honeycomb cores, honeycomb cores, are currently predominantly used for sandwich structures. These have an open structure in the thickness direction, ie in the direction of the cell opening 104 (see FIG. 1). Sandwich structures which use honeycomb cores are usually expensive to manufacture and thus expensive.

An alternative offer so-called folding honeycomb. Due to their continuous production process, these folded honeycombs are more economical to manufacture, offer adjustable mechanical properties due to variable folding geometries and have a drainage function running in a sandwich direction.

Although the core material has good tensile properties in the direction of the fiber orientation but less good properties transverse to the fiber orientation (so-called normal stress), the folded honeycomb structure can delaminate at a correspondingly high normal stress. Since an adhesion of folded honeycomb only acts on one side of the core, very high levels of normal forces occur, which often weakens the strength and stability of the connection of the folded honeycomb to the outer laminate layers. SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved sandwich structure with a folded honeycomb core.

A method for producing a sandwich structure with a folded honeycomb core, a tool for producing a sandwich structure with a folded honeycomb core, a sandwich structure for an aircraft and an aircraft with a sandwich structure according to the features of the independent claims are given. Further developments of the invention will become apparent from the dependent claims.

The described embodiments relate equally to the manufacturing process, the tool, the sandwich structure and the aircraft.

According to one embodiment of the invention, a method for producing a sandwich structure with a folded honeycomb core is specified in which an adhesive is applied in a first region and a second region of the sandwich structure. For example, the adhesive is applied to a honeycomb web of the folded honeycomb core. The adhesive is then positioned in the first region of the sandwich structure about the honeycomb web of the folded honeycomb core so that the adhesive on the second region of the sandwich structure is reduced.

In other words, in a first step, the adhesive is distributed at least on the outer surfaces of the honeycomb webs (which later communicate with the laminate material) and the intervening regions of the folded honeycomb core and then redistributed in a second step, so that the Emphasis collects where it actually needed most becomes. Of the places where it is not needed, it is deducted or removed.

Also, the adhesive may be applied to the inside of the laminate material prior to bonding the laminate material to the folded honeycomb core.

This can ultimately lead to a weight reduction of the finished sandwich structure, as the use of unnecessary adhesive is avoided.

The accumulation of the adhesive on the webs of the core material increases the strength of the sandwich structure, whereby the amount of adhesive or material used is optimally utilized.

By collecting the adhesive at the junctions between the honeycomb webs and the laminate, undercuts result which result in a positive fit. As a result, the connection of the folded honeycomb core to the cover skin (laminate) can be improved.

According to a further exemplary embodiment of the invention, the first region is a region at which the honeycomb web of the core material adjoins a cover layer of the sandwich structure. The second area is an area on the top layer that lies between two honeycomb webs.

According to a further embodiment of the invention, the adhesive is applied as a carrierless adhesive film on the Faltwabenkern, wherein the adhesive film is cut after application to the Faltwabenkern at defined locations to allow targeted positioning of the adhesive in the first region around the honeycomb web. The adhesive film is applied, for example, by a roller which presses the adhesive film against the honeycomb webs of the folded honeycomb core. By cutting the adhesive film at selected points is achieved that the adhesive film can nestle against the honeycomb webs.

According to a further embodiment of the invention, the cutting of the adhesive film by means of a laser beam or by means of a blade takes place.

Cutting with a laser beam has the advantage that the cutting tool does not have to be ground and that very fine cuts can be carried out. Furthermore, the control of the laser can be programmed so that different cuts, depending on the used honeycomb structure, can be generated.

According to a further embodiment of the invention, the adhesive film is melted after cutting by means of a hot air flow to the honeycomb web. Due to the hot air flow, it is possible to ensure that the areas of the adhesive film which are loose after the incisions are folded over in the desired direction and thus conform to the honeycomb webs. Then, for example, the Faltwabenkern be turned.

According to a further embodiment of the invention, the adhesive is admixed with a powder of magnetizable particles prior to its application to the honeycomb web (or to the laminate). The targeted positioning of the adhesive in the first region around the honeycomb web is then carried out at least partially by applying a magnetic field which exerts a force on the magnetizable particles. If the adhesive is a flowing adhesive, the flow of the adhesive may be affected by the magnetic field. If the adhesive is an adhesive film, the folding of the loose areas of the adhesive film after being cut by the magnetic field can be controlled. In this case, no hot air flow is required. Rather, heating is sufficient to melt the adhesive film on the webs.

According to a further exemplary embodiment of the invention, the field profile of the applied magnetic field is adjusted to a profile of the honeycomb web such that adhesive collects by the application of force of the magnetic field to the particles in the first region.

This may be, for example, a static magnetic field whose magnetic field lines are designed accordingly, so that the particles (together with the adhesive) migrate to the first region.

The magnetic field may also be a dynamic magnetic field, which is, for example, electrically changed in order to deflect the particles toward the webs.

For example, the magnetic field may also be generated by a magnet or an array of magnets (eg, permanent magnets), the magnet (s) being moved in a direction perpendicular to the honeycomb web.

In this way, the magnet takes the particles and thus the adhesive, so that an adhesive transport takes place towards the honeycomb web. According to a further embodiment of the invention, the folded honeycomb core is perforated at a kink before applying the adhesive.

This perforation is done for example by means of a milling cutter or a saw blade. Also, the perforation can be done by means of a laser.

Now when the glue is applied to the webs of the folded honeycomb core, it can flow through the resulting holes to collect in selected areas.

In this way, the stability of the finished sandwich structure can be further increased.

According to a further exemplary embodiment of the invention, a tool for producing a sandwich structure with a folded honeycomb core is provided which has a device for generating a magnetic field for the targeted positioning of an adhesive in a first region of the sandwich structure around a honeycomb web of the folded honeycomb core. The positioning takes place in such a way that the adhesive is reduced in a second area of the sandwich structure.

According to a further embodiment of the invention, the field profile of the magnetic field generated by the device is adapted to the course of the honeycomb web, so that the adhesive automatically collects in the first region.

According to a further embodiment of the invention, the device has at least one rod-shaped permanent magnet. According to a further embodiment of the invention, a sandwich structure for an aircraft is specified, wherein the sandwich structure is produced by the method described above.

According to another embodiment of the invention, there is provided an aircraft having a sandwich structure as described above made by the method described above.

In the following, embodiments of the invention will be described with reference to the figures.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows a schematic representation of a sandwich structure with a honeycomb core.

FIG. 2 shows a schematic representation of a sandwich structure with a folded honeycomb core according to an exemplary embodiment of the invention.

FIG. 3 shows a schematic cross-sectional representation of the sandwich structure of FIG. 2. FIG.

4 shows a schematic cross-sectional representation of the sandwich structure of FIG. 1.

Fig. 5 shows the glue line of a honeycomb core.

Fig. 6 shows the glue line of a folded honeycomb. FIG. 7 shows a micrograph of a seam seam on a honeycomb core. FIG.

FIG. 8 shows a working step of a retraction method for honeycomb cores.

9 shows an illustration of an incised adhesive film in front of the

Melting with a hot air film according to an embodiment of the invention.

Fig. 10 shows an adhesive accumulation on the honeycomb webs of a folded honeycomb after curing according to an embodiment of the invention.

Fig. 11 shows a tool according to an embodiment of the invention.

Fig. 12a shows an adhesive accumulation caused by the tool of Fig. 11. Fig. 12b shows a further accumulation of adhesive by the tool of the

Fig. 11 is caused.

Fig. 13 shows a perforation made by milling on the honeycomb webs according to an embodiment of the invention.

14 shows a flowchart of a method according to an embodiment of the invention.

Fig. IS shows an aircraft according to an embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS

The illustrations in the figures are schematic and not to scale.

In the following description of the figures, the same reference numerals are used for the same or similar elements.

1 shows a schematic representation of a sandwich structure 100 with a honeycomb core 101. Above and below the core 101, cover layers 103, 102 are arranged. The core structure 101 and also the

Core structures of the other figures typically consist of aramid fibers (paper) and a phenolic resin impregnation, especially for aerospace applications. The structure does not allow drainage within the closed sandwich due to its thickness-direction open structure 104.

FIG. 2 shows a sandwich structure 200 with a folded honeycomb 201. The arrow 204 shows the direction of the cell opening. Again, above and below the Faltwabe

201 cover layers 203, 202 provided to form the sandwich structure. The closed in the thickness direction structure (drainage function in the direction 204) leaves the adhesive side only one-sided access to the core material, which is designated in Fig. 3 by the reference numerals 302, 303, 306 and 307.

Fig. 3 shows the webs 301, 304 of a folded honeycomb, which is between the laminate layers

202 and 203 are arranged. The Lamiatschichten 202, 203 are wetted on their inner sides 309, 310 with adhesive. The folding honeycomb is only wetted with adhesive on its respective outside. Thus, the folded honeycomb is wetted at the top only in the areas 302, 303, but not in the area 305th Accordingly, the Faltwabe wetted on its underside only in the areas 306, 307, but not in the area 308.

The one-sided load and the associated high proportion of normal forces that can occur in such a sandwich structure, can lead to a failure of the bond between the phenolic resin and the aramid paper.

Fig. 4 shows a schematic cross-sectional view of a sandwich structure with a Honeycomb honeycomb. The webs 401, 404 of the Honeycomb honeycomb are wetted on both sides with adhesive 402, 403, 405, 406.

Fig. 5 shows an adhesive line of a Honeycomb honeycomb.

FIG. 6 shows the glue lines 601, 602, 603 of a folding honeycomb of comparable cell width.

Compared with a honeycomb core sandwich structure, the surfaces of the existing glue lines in the folding honeycombs are significantly smaller than in the case of the normal honeycomb honeycomb cells with comparable cell width (see FIGS. 5 and 6). Only along the existing bond lines is a contact between the core material and the cover layers 202, 203 with the adhesive layer possible.

As is clear from the comparison of FIGS. 5 and 6, the surface or the length of the glue lines of the folded honeycomb is significantly lower than that of the Honeycomb honeycomb. In order to increase the stability of the sandwich structure, the fillet weld seam can be made more pronounced, so that the adhesive surface is increased so that the forces can be better introduced into the core.

FIG. 7 shows a micrograph of fillet weld formation on a honeycomb core. FIG. It can be seen the honeycomb web 401, which is embedded in the adhesive film 701 by means Kehlnat 402. In general, an adhesive film 701 is provided with a substrate. The fillet 402 provides a connection of the honeycomb web 401 to the laminate 102. Reference numeral 702 shows the investment material used for sample preparation.

The types of adhesives predominantly used for sandwich components are thermosetting films with a carrier material (eg polyamide fabric). Such adhesive films offer the possibility to keep the amount of adhesive over the entire component surface constant and thus sufficient adhesive everywhere

To make available. Wet areas between the bars are often useless additional weight and are not needed. This is particularly important in the case of folding honeycombs, as the areas affected between the bars are even larger here than in honeycomb structures.

In order to achieve a desired distribution of the adhesive on honeycomb webs in honeycombs, as shown in FIG. 8, strapless adhesive films may be used, whereupon a so-called reticulation process is carried out. For this purpose, a hot air stream is passed through the honeycomb. The applied adhesive film is liquefied by the heat and is formed by the air flow to a bubble. As the heating increases, the wall thicknesses of the bubble become thinner and thinner until the bubble 801 is destroyed. Subsequently, the entire adhesive is applied to the honeycomb webs. One of the working steps of a retraction method is shown in FIG. A prerequisite for the functioning of this method, in addition to the open cells of the core material is a carrier-free adhesive film 801, which can be melted. Due to its closed structure, however, this method is not applicable to folding honeycomb.

The folding honeycombs used for the sandwich structure according to the invention can be produced by means of a biaxial embossing piotr (X-Y plotter) which produces the kink edges of the honeycombs. This method offers the possibility of being able to flexibly design the folding geometries of the folding honeycomb. The tool costs are low.

Also, the embossing piotter can be used to impress small pores in the creases (see Fig. 13). These should later give the adhesive the opportunity to flow at these points through the honeycomb material and form an undercut after curing. Such a form fit has advantages for the mechanical properties of the sandwich structure.

If, however, a rolling technique is involved in the production of the sandwich structure, it may happen that the pores are closed again by the curing of the phenolic resin, which always has to take place after embossing and "placing" the honeycomb.

In the following three methods for the production of an optimized adhesive connection of folded honeycomb cores in sandwich structures are described, with the help of which the sandwich structures can be produced. The methods described below can also be combined with each other. Retraction method for folded honeycomb:

The sandwich structure with folded honeycomb core can be created by a combination of carrierless adhesive film, specific cutting of the adhesive film and heating of the adhesive film.

In this case, an adhesive film is applied to the Faltwabenstege. However, the adhesive film has no carrier fleece. The adhesive film is, for example, 3M Scotch-Weld ™ AF163-2U Wt.06.

After the adhesive film has been applied to the core material and possibly lightly pressed with the aid of heat (for example by means of a laminating roller), the adhesive film is cut in certain places. The cutting takes place, for example, along the valleys of the folded honeycomb (see FIG. 9). In this way, the adhesive can be forced to contract.

The cutting takes place for example with the aid of a cutting tool (for example a knife) or by means of laser irradiation. For the further procedure is between

Laminate top and laminate bottom distinguished, so that an upper and lower splice are formed.

FIG. 9 shows a representation of a folded honeycomb structure with an incised adhesive film (for the underside of the sandwich structure) applied to it

Melting with a hot air blower. For example, the adhesive film 901 is cut in at the region 903, so that loose regions 902 of the adhesive film are formed, which are not yet supported by the webs of the folded honeycomb. Due to the effect of gravity, the adhesive film is cut longitudinally and transversely to the honeycomb on the later underside of the sandwich structure and slightly fused with a Heißluftföhn or blower, so that the adhesive can already largely put on the webs. Now, the prepared core is turned over and applied to the lower cover skin (laminate) of the sandwich structure (see, for example, reference numeral 202 of FIG. 3).

Now you can start with the upper gluing. For this purpose, the upper side is first again fitted with an adhesive film and pressed. After re-cutting the film (here only the longitudinal cuts are necessary), it is possible in contrast to the bottom directly on the upper cover skin 203, without the need for a Heißluftföhn must be used because the gravity prevents sticking of the loose adhesive film to the upper cover skin , The curing of the adhesive film is then again using standardized methods. As a result, an up to five times higher peel strength compared to the closed standard film adhesive can be achieved.

Fig. 10 shows the adhesive accumulation on the webs 601, 602 of a folded honeycomb after curing. As can be seen from FIG. 10, the adhesive film has nestled against the side edges 1001, 1002 of the webs.

Magnetic adhesive:

Another way to position the adhesive on the honeycomb webs is to use magnetic fields. For this purpose, the adhesive magnetic particles, for example in the form of so-called. Nanoferriten be mixed, which make the adhesive magnetizable. The nanoferrites can be MagSilica particles of the Degussa trade. But there are also other particles from other manufacturers usable.

In order to achieve sufficient magnetizability, the adhesive is mixed with two to fifteen percent by weight. The weight ratio depends, for example, on the viscosity of the adhesive. The thinner a resin (adhesive) is, the fewer nanoferrites are needed to move the adhesive. With increasing ferrite content, the forces acting on the adhesive also increase. In addition, the filler content also has an influence on the viscosity. The viscosity also increases with the proportion of the filler. Depending on the application, others will

Percent by weight of the particles admixed in order to set an optimum of increasing force and decreasing mobility (ie increasing viscosity).

The prepared adhesive can now be applied evenly to the cover skin. This can be done by means of rolling or doctoring. After placing the folding honeycomb a special tool for distributing the adhesive is used.

Fig. 11 shows a schematic representation of the tool according to an embodiment of the invention. The tool 1100 comprises magnetic tracks 1101, 1102, 1103, which are arranged according to the zigzag shape of the folds of the folded honeycomb (see FIG. 6). The magnetic paths are formed, for example, in each case by the poles of a corresponding bar magnet. Now, if the sandwich component is placed on the tool and the tool is aligned so that the magnetic field lines can act on the kinks, the adhesive can be accumulated at the kinks where it is needed. Furthermore, the tool has a frame with a holding portion 1104, which serves to guide the tool. In other words, the adhesive is transported through the magnetic field. The magnetic fields can be generated by one or more permanent magnets or by an electromagnet (or a combination of permanent and electromagnets).

In a simple embodiment, the tool has only a single linear magnet or bar magnet, which is pulled along under the sandwich structure. For example, the magnet is aligned parallel to the drainage direction (see arrow 204 of FIG. 2) and is moved perpendicular to the drainage direction. By moving the magnet, the adhesive is collected according to the field lines and pulled along. When hitting the continuous honeycomb web, the adhesive remains at the point of impact, so that then forms a fillet weld. On the other side of the bridge, the process begins again.

In this way, for example, an accumulation of adhesive on each side of the webs done. An advantage of this method lies in the production of semi-finished products in a continuous production process.

Figs. 12a and 12b show adhesive accumulations 1201 and 1202 which have been created by the magnetic forces of such a tool.

Perforated honeycomb webs:

In particular, this method can be combined with the two aforementioned methods. It is introduced with a cutter having a diameter of, for example, 0.5 to 1 mm, a perforation in the bending point of the folded honeycomb. FIG. 13 shows such a perforation on the honeycomb webs 601 produced by milling. The honeycomb webs 601 have perforation holes 1301, 1302 or perforation slots on their upper and lower sides.

The same effect can be achieved by a saw blade of appropriate thickness. Depending on the viscosity of the adhesive, the depth and the width of the cut, an undercut forms after the adhesive has set. Such a positive fit, similar to a zipper, can significantly increase the strength of the finished sandwich structure.

14 shows a flowchart of a method according to an embodiment of the invention. In step 1, adhesive is applied to the honeycomb webs of a folded honeycomb core. In step 2, the adhesive in the areas where the honeycomb webs contact the laminate cover layers is collected and removed from the areas where it is not needed.

In step 3, the adhesive is then cured.

The targeted positioning of the adhesive after application, for example, by a combination of magnetic force exerted on particles contained in adhesive and the guidance of the accumulated adhesive through appropriate perforations.

Fig. 15 shows an aircraft 1500 with sandwich structures according to a

Embodiment of the invention. The aircraft is a passenger aircraft. The sandwich structures 1501 are used, for example, to reinforce the hull. In addition, it should be noted that "comprehensive" and "comprising" do not exclude other elements or steps, and "a" or "an" does not exclude a multitude. It should also be appreciated that features or steps described with reference to any of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be considered as limitations.

Claims

claims

A method of making a sandwich structure (200) having a folded honeycomb core (201), the method comprising the steps of: applying an adhesive in a first region (302) and a second region

Area (309) of the sandwich structure (200); selectively positioning the adhesive in the first region (302) of the sandwich structure (200) about a honeycomb web (301) of the folded honeycomb core (201) such that the adhesive is reduced at the second region (309) of the sandwich structure (200).

The method of claim 1, wherein the first region (302) is a region where the honeycomb web (301) of the core material joins a cover layer (202, 203) of the sandwich structure (200); wherein the second region (309) is an area on the cover layer (202, 203) that lies between two honeycomb webs (301, 304).

3. The method of claim 1 or 2, wherein the adhesive is applied as a strapless adhesive film on the Faltwabenkern (201); wherein the adhesive film, after being applied to the folded honeycomb core (201), is cut at defined locations (903) to permit the targeted positioning of the adhesive in the first region (302) about the honeycomb web (301, 304).

4. The method according to any one of the preceding claims, wherein the cutting of Klebefims carried out by means of a laser beam.

5. The method according to any one of the preceding claims, wherein the adhesive film is melted after cutting by means of a hot air flow to the honeycomb web (301, 304).

6. The method according to any one of the preceding claims, further comprising the step:

Admixing of magentazable particles to the adhesive prior to its application to the honeycomb web (301, 304); wherein the targeted positioning of the adhesive in the first region (302) about the honeycomb web (301, 304) is at least partially accomplished by applying a magnetic field which exerts a force on the magenta particles.

7. The method of claim 6, wherein a field profile of the applied magnetic field so on a course of the

Honeycomb web (301, 304) is adapted that adhesive collects by the application of force of the magnetic field to the particles in the first region (302).

A method according to claim 6 or 7, wherein the magnetic field is generated by a magnet (1101, 1102, 1103) which is moved in a direction perpendicular to the honeycomb web (301, 304).

The method of any one of the preceding claims, further comprising the step of: perforating the folded honeycomb core (201) at a kink in front of

Apply the adhesive.

10. The method of claim 9, wherein the perforation is performed by a milling cutter or a saw blade.

11. The method according to any one of the preceding claims, wherein the sandwich structure (200) is intended for use in an aircraft.

12. A tool (1100) for producing a sandwich structure (200) with a folded honeycomb core (201), the tool comprising: a device (1101, 1102, 1103) for generating a magnetic field for selectively positioning an adhesive in a first region (302) of Sandwich structure (200) around a honeycomb web (301, 304) of the folded honeycomb core (201), so that the adhesive is reduced at a second region (309) of the sandwich structure (200).

13. The tool according to claim 12, wherein a field profile of the magnetic field generated by the device is adapted to a profile of the honeycomb web (301, 304) such that adhesive collects by the application of force of the magnetic field to the particles in the first region (302).

14. Tool according to claim 12 or 13, wherein the device comprises a rod-shaped permanent magnet (1101, 1102, 1103).

A sandwich structure (200) for an aircraft manufactured by a method according to any one of claims 1 to 11.

16. An aircraft with a sandwich structure (200), which is produced by a method according to one of claims 1 to 11.